1. Field of the Invention
This invention relates generally to valve timing varying devices which are used for advancing and/or retarding the phased camshaft to crankshaft relationship in internal combustion (I.C.) engines during operation.
2. Description of the Related Art
State of the art valve timing-varying devices which are used primarily for automotive I.C. engines are either very complex in nature or made up of components that are short lived or beset with operational problems. These devices are generally a hybrid of complex electro-mechanical or hydro-mechanical systems which by their character depend on component-dense electronic subsystems for precisely controlling the phased camshaft to crankshaft position on demand. While they improve engine performance and provide more economical vehicle operation, the advantages gained are offset by the costs of system failures and maintenance. Mechanisms disclosed in U.S. Pat. No. 3,978,829 to Takahashi, and U.S. Pat. Nos. 4,494,495, 4,494,496 and 4,561,390 to Nakamura et al. are highly complex self-adjusting gear means and heavily dependent on component-dense subsystems for operation. They are costly to manufacture and to maintain in reliable operating condition. Along with the needed electronic signal generating sensors, signal processing computers and other related controls, they are also excessively bulky and their substantially overhanging size tends to expand the engine's overall length. Also, U.S. Pat. No. 4,754,727 to Hampton besides being dependent on complex automotive electronics, this system is beset by problems generally associated with rotating electro-mechanical systems which operate in extremely hostile environments. In hydro-mechanical arts which are disclosed in U.S. Pat. Nos. 4,627,825 to Bruss et al., 4,535,731 to Banfi, and 4,787,345 to Thoma, their overall functional reliability is greatly reduced by their complex electronic controls and costly hydraulically operated components. Yet in other arts comprising spherical or cylindrical flyweights to accomplish angular changes, these devices are plagued with problems associated with high unit loads being concentrated on relatively small sliding surfaces which directly effect the system's operating life cycle and functional reliability U.S. Pat. No. 5,090,365 to Hotta et al. includes mated labyrinth grooves on component surfaces as hydraulic dampers and integrated electronic control systems which require costly maintenance In an all hydraulically operated device as disclosed in U.S. Pat. 4,858,572 to Shirai et al., the actuating vanes lack the positive seals which are necessary for precisely maintaining angular position under all operating conditions. The above referred systems are excessively costly to manufacture, expensive to maintain, and by their character have only marginal system reliability.